This invention relates to a color display tube comprising a display window with a circumferential upright edge and corner areas, a color selection electrode comprising corner sections to which suspension means are coupled, which is suspended from supporting elements, secured to the corner areas.
The invention also relates to a color selection electrode for use in such a color display tube and to a corner section for use in such a color selection electrode.
A color display tube as described in the opening paragraph is disclosed in U.S. Pat. No. 5,003,218. The color display tube according to this specification is provided with a color selection electrode having a frame consisting of four diaphragm parts and four corner sections, suspended in the corners of the display window.
The color selection electrode serves to make sure that each electron beam coming from three electron guns mounted in a neck portion of the tube only excites the electroluminescent material of the appropriate color on the inner side of the display window. This color selection is achieved by applying, for instance, a shadow mask in the tube. This shadow mask comprises a pattern of apertures arranged in most cases in either a slotted pattern or a dotted pattern. If the color selection electrode is not stably positioned in the color display tube, small deviations from its position will lead to a deterioration of picture quality. If the color selection electrode is shifted slightly, for instance due to vibrations, the shadowing effect of the color selection electrode changes and consequentially, the electron beams do not hit the appropriate electroluminescent material on the display window. These misregistrations cause discoloration of the color display tube that lead to a deterioration of the quality of the picture.
Color display tubes with a color selection electrode as disclosed in U.S. Pat. No. 5,003,218 show in practice discolorations due to vibrations that are too large to fulfil the ever-increasing demand for picture quality. Especially wide screen tubes and tubes with a real flat or almost flat outer surface of the display window are affected by these problems. It is a disadvantage of the known color display tube that it shows misregistrations that are too large.
It is an object of the invention to provide a color display tube having a color selection electrode with an improved behavior with respect to color purity that overcomes the disadvantages of the prior art color display tube.
According to the present invention, this object is realized by means of a color display tube which is characterized in that a vibration damping element is coupled to the suspension means.
The invention is based on the insight that the color purity of the color picture tube is improved when vibrations which come from outside the color display tube cannot reach the shadow mask. These vibrations may be caused by, for instance, loudspeakers that are mounted in the cabinet or by other shocks exerted on the color display tube. The transfer of vibrations from the outside to the color selection electrode takes place via the suspension means of the color selection electrode in the display window. The general idea is to provide the suspension means with an element for damping the vibrations of especially those frequenciesxe2x80x94the resonance frequenciesxe2x80x94to which the color selection electrode is most sensitive. In this way the incoming vibrations will not be able to reach the color selection electrode and the color purity performance of the color display tube is improved.
In a preferred embodiment, the suspension means further comprise a resilient element, the vibration damping element being coupled to the resilient element.
In order to have a good suspension of the shadow mask in the display window, the suspension means are provided with a resilient element. The spring forces between the resilient elements and the supporting elements make sure that the shadow mask stays in the proper position in the color display tube. Vibrations coming from the outside can only be transferred to the shadow mask if they can pass these resilient elements. So, the best way to suppress these vibrations is by arranging the vibration damping element so as to be in contact with the resilient element in such a way that if the resilient element starts vibrating, this vibration energy is transferred to the vibration damping element and the amplitude of the vibration is extinguished.
In a further embodiment, the vibration damping element is positioned on the side of the suspension means facing the supporting element. Furthermore, it is plate-shaped having a first edge for rigidly coupling it to the resilient element and a second edge which is in contact with the resilient element and it is provided with a bend line extending substantially parallel to the first edge and the second edge and positioned between them.
This embodiment provides an advantageous way of constructing a vibration damping member. A plate-shaped element can be arranged parallel to the resilient element in such a way that a rigid connection is obtained at one side of the plate shaped element, while the other side is in free contactxe2x80x94due to the spring forcexe2x80x94with the resilient element. The direction in which the resilient element is pushed when the color electrode is in its position in the color display tube makes it necessary to provide the vibration damping member with a bend in order to make sure that the side that is in free contact stays in contact.
Alternatively, in another embodiment the suspension means further comprise a rigid portion, and the vibration damping element is plate-shaped and positioned in between the rigid portion and the resilient element.
Here, the vibration element is positioned on the other side of the resilient element. Seen in the direction of the spring forces in the resilient element, a bend line in the vibration damping element is not required here.
The invention further relates to a color selection electrode for use in such a color display tube and to a corner section for use in such a color selection electrode.